This application relates to rotors for use in gas turbine engines, where purge blades generate a pressure to resist ingestion of hot gas.
Gas turbine engines are known, and typically include a compressor compressing air, and delivering the air into a combustion section. The air is mixed with fuel and combusted in the combustion section. Products of this combustion pass downstream over turbine rotors. The turbine rotors may include a rotor with removable blades. Alternatively, integrally bladed rotors wherein the rotor and the blades are formed as one, are also known.
In addition to the flow of hot combustion products across the turbine rotors, cool air is also delivered. The cool air serves to cool the rotor and blades, since they operate in a very high temperature. In addition, another purpose of the cool air is to provide a “purge” flow which resists the ingestion of the hot combustion products into the area of the rotor and blade interface. As an example, in one type removable blade, a so-called “fir-tree” includes a plurality of segments which are inserted into corresponding fir-tree grooves in the rotor. The blade is held into the disc by locking features such as a clip or rivet.
However, at times, if the hot gas combustion products are ingested into the area of the fir-tree, there can be challenges raised. As one example, a concern known as both blade and disc creep occurs when there is plastic deformation of the blade and disc. This can occur if they are subjected to temperatures beyond a material creep resistance capability.
Another concern is so-called “blade walking.” Blade walking typically occurs at startup of the gas turbine engine when there may be insufficient cooling air. The blade will heat more rapidly than the rotor, and thus the blade may move axially within the groves in the rotor. That occurs since the difference in thermal gradient between the disc and blade at the fir-tree gives rise to forces that overcome the strength of the locking features holding them together. As a consequence relative motion between disc and blade takes place. This is known as blade-walking.
Both of the above occurrences are undesirable.